1. Field of the Invention
The present invention relates to a semiconductor humidity sensor.
2. Description of the Related Art
As a conventional capacitive humidity sensor, a circuit as shown in FIG. 5 has been known (see, for example, FIG. 1 of JP 2003-156464 A).
In FIG. 5, comb-shaped electrodes are formed on a substrate. The electrodes are coated thereon with a humidity sensitive film whose dielectric constant varies depending on humidity. The humidity sensitive films are inserted between the comb-shaped electrodes. An approximate capacitance C between the electrodes 21 and 22 can be obtained by the following equation (1):C=∈0·∈H·S/dH  (1)
where dH is an interval between electrodes 21 and 22, S is an area where the electrodes 21 and 22 are opposing each other, ∈H is a dielectric constant of the humidity sensitive film between the electrodes 21 and 22, and ∈0 is the permittivity of vacuum.
Change in the dielectric constant ∈H of the humidity sensitive film between the electrodes on humidity causes change in the capacitance C between the electrodes 21 and 22, thus measurement of the capacitance C enables the measurement of humidity.
In addition, as a circuit similar to that of FIG. 5, a resistance type humidity sensor has been known (see, for example, FIG. 1 of JP 08-145932 A). In the resistance type humidity sensor, a humidity sensitive film whose resistivity varies depending on humidity is coated onto the electrodes 21 and 22 (between the electrodes 21 and 22), in place of the above-mentioned humidity sensitive film whose dielectric constant varies depending on the humidity. In this case, a resistance between the electrodes 21 and 22 varies depending on humidity, thus measurement of the resistance enables the measurement of humidity.
Poor adhesion property between the humidity sensitive films on the electrode and between the electrodes and the substrate in the conventional humidity sensor raises a problem of easy peeling off of the humidity sensitive film. In addition, there is a problem in that a humidity distribution in a minute area cannot be determined.